Polymerization process



Patented Aug. 15, 1950 POLYMERIZATION PROCESS Ralph Albert Jacobson,deceased, late of Landenberg, New Garden Township, Chester County, Pa.,by Winifred M. Jacobson, executrix, Landenberg, Pa., assignor to E. I.du Pont de Nemours and Company, Wilmington, Del., a

corporation of Delaware No Drawing. Application June 4, 1948, Serial No.31,209

12 Claims. (Cl. 260-88-7) This invention relates to the manufacture ofpolymers and more particularly to novel processes for the production ofhomopolymers and copolymers of monoethylenic monomers. More specificallyit relates to a new and improved process for the polymerization ofpolymerizable monoethylenic vinylidene compounds having a molecularweight greater than 30, in which the sole allphatic carbon-to-carbonunsaturation is the double bond in thevinylidene radical.

This application is a continuation-in-part of copending applicationSerial No. 458,734, filed September 17, 1942, now U. S. Patent2,462,354.

Within recent years the plastics industry has utilized a wide variety ofpolymeric materials in the production or manufacture of a wide varietyof valuable commercial articles. Rapid progress has been made on theimportant problem of developing improved techniques for the preparationof these polymers. Nevertheless, the polymerization of monoethyleniccompounds and more particularly monoethylenic. vinylidene compoundshaving a molecular weight greater than 30 in which the sole aliphaticcarbon-to-carbon unsaturation is the double bond in the vinylidene orHzC=C= radical, is often a slow, uneconomical process which cannot beapplied efliciently to manufacture on a large commercial scale. As aresult, many polymers having attractive properties have been produced inthe laboratory but have never been prepared commercially because of thelack of suitable methods for their production. Moreover, some of themost valuable polymers of this class are not homopolymers, i. e., madefrom a single monomeric component, but arerather copolymers produced bythe copolymerization of two or even more such polymerizable monomers. Inthi case the problem of obtaining satisfactory products is furthercomplicated by difliculties in obtaining homogeneous products. Forexample, the copolymerization of dilferent aforesaid vinylidenecompounds with or without other monoethylenic compounds frequentlyproceeds at different rates; hence non-homogeneous copolymers ofinferior quality as evidenced by opacity, low softening point or otherundesirable qualities are obtained. This invention which provides anovel, eflicient and practicable process for overcoming the diflicultiesattending known polymerization techniques accordingly represents an'important advance in theart of producing polymers.

This invention has as an object the provision of an improved process forpolymerizing polymerizable monoethylenic vinylidene compounds having amolecular weight greater than 30 in which the sole aliphaticcarbon-to-carbon unsaturation is the double bond in the vinylideneradical, i. e., the

H2C=C= radical. Another object is to provide an extremely rapid andcontrollable process for the polymerization of such compounds eitheralone or in admixture with other monoethylenic compounds. Additionalobjects will become apparent from an examination of the followingdescription and claims.

These and other objects and advantages are accomplished according to thehereindescribed invention which broadly comprises forming an aqueousmixture containing one or more monoethylenic monomers having a molecularweight greater than 30 in which the sole aliphatic carbon-to-carbonunsaturation is the ethylenic double bond (at least 5% by weight of suchmonoethylenic monomeric material being a polymerizable vinylidenecompound in which the sole aliphatic carbon-to-carbon unsaturation isthe double bond in the vinylidene radical), said aqueous mixturecontaining from 0.01% to 5% of an oxygen-yielding polymerizationcatalyst and from 0.001% to 5% of a sulfinic acid or an alkali metalsalt thereof, said percentage amounts being based upon the total weightof monoethylenic monomeric material present in the aqueous mixture, andmaintaining the resultant aqueous system at a temperature of from 0 C.to C. until polymerization has taken place.

In a more restricted sense this invention consists in subjecting one ormore polymerizable monoethylenic monomeric vinylidene compounds having amolecular weight greater than 30 in which the sole aliphaticcarbon-to-carbon unsaturation is the double bond in the vinylideneradical in an aqueous medium containing from 0.01% to 5% of anoxygen-yielding polymerization catalyst and from 0.001% to 5% of asulfinlc acid or an alkali metal salt thereof, based on the total weightof the vinylidene compound or compounds, to a temperature of from 0 C.to 125 C. until polymerization has taken place.

In one preferred embodiment of this invention a polymerizable monomericmonoethylenic vinylidene compound having a molecular weight greater than30 in which the sole aliphatic carbon-to-carbon unsaturation is thedouble bond in the vinylidene radical, or a mixture of said vinylidenecompounds containing at least 5% by weightof one such compound, is addedto water containing from 0.1% to 2% of an oxygen-liberating catalystsuch as hydrogen peroxide, benzoyl peroxide or a soluble salt ofperdisulfuric acid, from 0.05% to 0.5% of a sulfinic acid or an alkalimetal salt thereof, such as formamidine sulfinic acid, or sodiump-toluene sulfinate, and optionally from 1% to of a suitable dispersingagent, theaforesaid percentage amounts being based upon the total weightof the vinylidene compound or compounds present in the aqueous mediumand the whole being contained in a reaction vessel provided with meansfor effective agitation. The reaction vessel is closed, the air in thefree space above the liquid is displaced by an inert gas such asnitrogen. The temperature of the reaction mixture is adjusted to anappropriate temperature between 0 C. and 125 C. and the reaction mixtureis agitated. These conditions are maintained until polymerization isessentially complete, usually in the neighborhood 01 from one to fivehours, or until polymerization has reached the desired extent. Thereaction product is then discharged; the unreacted monomer, if any, isremoved by steam distillation and the polymeric product is coagulated byadding a solution of electrolyte such as aluminum sulfate. Thecoagulated product is filtered, washed thoroughly to remove traces ofimpurities and residual dispersing agent and is finally dried.

The following examples in which proportions are in parts by weight,unless otherwise specified, are given for illustrative purposes and arenot intended to place any restrictions on the hereindescribed invention:

Example I A mixture of parts of acrylonitrile and a solution of 0.1 partof ammonium perdisulfate and 0.02 part of sodium p-toluenesulfinate in30 parts of water is charged into a reaction vessel which is thenflushed with nitrogen to displace the air, closed and rotated end overend at a temperature of 29 C. Polymer first begins to separate after 8minutes, and the polymerization is substantially complete after 143minutes.

Example II A stainless steel oscillating autoclave is charged with 50parts of vinyl acetate and a solution in 150 parts of deoxidized waterof 0.5 part of ammonium perdisulfate, 2 parts of a commercial dispersingagent containing about 32% of the sodium salt of sulfonated parafiinwhite oil as the active ingredient, 1 part of sodium dihydrogenphosphate and 0.1 part of formamidine sulfinic acid, the pH of thissolution being adjusted to 6.4 with sodium bicarbonate. The vessel isflushed with nitrogen, sealed and pressured with propene gas to apressure of 100 lbs. per square inch. The autoclave is then rocked in awater bath at 60 C. for 8 hours, after which the residual pressure isreleased and the contents of the vessel discharged. The reaction productis a smooth polymer emulsion which is treated with 0.5 part ofhydroquinone to prevent further polymerization of any unreacted vinylacetate. The pH of the mixture at this point is 5.4. The mixture issteamed to remove any unreacted monomer and coagulated hot by additionof aluminum sulfate solution. The polymer is milled on a wash mill withcorrugated rolls under a stream of cool water until the dispersing agentis removed, sheeted out on the mill and the sheet cut up in fine piecesfor drying. There is thus obtained 51.5 parts of a copolymer of vinylacetate and propene.

Example III Sixty parts methyl methacrylateis mixed with 4 an aqueoussolution consisting of 133.8 parts of water, 1.5 part of 30% hydrogenperoxide, 0.6 part of sodium p-toluenesulflnate, 0.38 part ofconcentrated hydrochloric acid and, as dispersing agents, 3.6 parts oftechnical sodium dodecyl sulfate and 0.45 part of the sodium salt of asulfonated naphthalene-formaldehyde reaction product. The mixture isheated in a sealed vessel under nitrogen at 45 C. for 141 hours. Aftersteaming, coagulating, filtering and drying, there are obtained 60 partsyield of light colorecd polymethyl methacrylate softening at Example IVA solution of 0.25 part of ammonium perdisulfate and 0.125 part offormamidine sulfinic acid in 100 parts of water is adjusted to pH 2.5 byaddition of dilute sulfuric acid, placed in a vessel and frozen byimmersion in a carbon dioxide-acetone bath. The vessel is swept withnitrogen, 51.8 parts of vinyl chloride are added, the vessel is sealed,warmed to room temperature. then placed in a bath at 40 C. After 2 hoursthere are obtained 15.9 parts of polymerized vinyl chloride.

' Example V A mixture of 200 parts of vinyl'acetate, 192 parts of water,16 parts of polyvinyl alcohol and 0.2 part of formamidine sulfinie acidis stirred under reflux condenser at a temperature of 44 C., and 1.25parts of 10% hydrogen peroxide are added in increments of 0.05 to 0.5part over a period of 57 minutes. An additional 0.3 part of formamidinesulfinic acid is added during that time. Rapid polymerization is shownby the fact that the reaction temperature increases to 61 C. during thereaction. After 73 minutes, 97% of the vinyl acetate is polymerized.This compares to 4-6 hours necessary to complete polymerization whenhydrogen peroxide alon is used as the catalyst.

While this invention has been illustrated with particular reference tothe polymerization of acrylonitrile, methyl methacrylate, vinylchloride, vinyl acetate and of a mixture of vinyl acetate and propene,it is to b understood that it is broadly applicable to thepolymerization of any and all monomeric monoethylenic vinylidenecompounds (1. e., compounds containing the terminal radical H2C=C=) thatare polymerizable, i. e., polymerizable according to one or more priorart processes (such as the process disclosed in U. S. Patent No.2,278,415, granted April 7, 1942), that have a molecular weight greaterthan 30 and in which the sole aliphatic carbon-to-carbon unsaturation isthe double bond in the vinylidene radical. In other words this inventionis applicable to all polymerizable monoethylenic compounds having theethylenic double bond in the terminal position, i. 6., com poundscontaining a terminal methylene group,

that have a molecular weight greater than 30 and in which the solealiphatic carbon-to-carbon unsaturation is the double bond in the HzC=C=radical.

Representative compounds of this class are acrylic and methacrylicesters, acrylic and methacrylic acids, acrylonitrile, methacrylonitrile,acrylic and methacrylic amide, styrene, vinyl naphthalene, vinylchloride, vinyl bromide, asymmetrical dichloroethylene, vinyl acetateand vinyl esters of higher carboxylic acids, methyl vinyl ketone, phenylvinyl ketone, methyl isopropenyl ketone, methylenemalonic esters,N-vinylphthalimide, N-vinylsuccinimide, vinyl thiolacetate,

- merized either alone to produce homopolymers or-in admixture with oneor more of said vinylidene compounds to produce copolymers.

In addition any other monomeric monethylenic compound having a molecularweight greater than 30in which the sole aliphatic carbon-tocarbonunsaturation is the ethylenic double bond "can be employed singly oradmixed with other such compounds in the instant process asinterpolymerization modifiers to bring about the production of manyvaluable products even though many such monoethylenic compounds eitherfail to polymerize or polymerize only to a limited extent or extremelyslowly in the presence of oxygen-liberating catalysts according to priorart processes. It is essential to this invention, however, that one ofthe members of themixture of monomeric monethylenic compounds subjectedto polymerization according to this invention should be a polymerizablevinylidene compound having a molecular weight greater than 30 in whichthe sole aliphatic carbon-tocarbon unsaturation is the double bond inthe vinylidene radical. Among examples of monomeric monoethyleniccompounds, other than the aforesaid vinylidene compounds, adapted foruse as modifiers in this invention may be mentioned fumaric esters, suchas methyl fumarate and ethyl fumarate, maleic esters, such as propyl andbutyl maleates, mesaconic esters, such as amyl' and hexyl mesaconates,citraconic esters such as methyl and amyl citraconates,N-vinylmaleimide, olefin hydrocarbons, such as 2-butene, andtrichlorethylene.

The most important classes from the industrial standpoint ofpolymerizable monethylenic monomeric vinylidene compounds having amolecular weight greater than 30 in which the sole aliphaticcarbon-to-carbon unsaturation is the double bond in the vinylideneradical are:

(1) The vinyl esters of saturated monocarboxylic acids, e. g., vinylformate, vinyl acetate,

vinyl propionate, vinyl stearate and the like;

(2) The vinyl halides, such as vinyl fluoride, vinyl chloride, vinylbromide and vinyl iodide;

(3) The esters of alpha, beta-unsaturated monocarboxylic acids in whichsaid alphabetaunsaturation is a terminal double bond and is the solealiphatic carbon-to-carbon unsaturation, such as methyl acrylate, ethylacrylate, propyl acrylate, methyl methacrylate, methylalphachloroacrylate and the like; and

(4) The alpha,beta-unsaturated nitriles in which saidalphabeta-i"nsaturation is a terminal double bond and is the solealiphatic carbonto-carbon unsaturation, such as acrylonitrile,methacrylonitrile and the like.

This invention is, therefore, of particular importance as regards thepolymerization of monomers belonging to the aforesaid classes and ofmixtures of such monomers.

In preparing copolymers, according to this in vention, of one or morepolymerizable monoethylenic monomeric vinylidene compounds having amolecular Weight greater than 30 in which the sole aliphaticcarbon-to-carbon unsoturation is the double bond in the vinylidene groupwith one or more other monoethylenic monomers having a molecular weightgreater than 30 in which the sole aliphatic carbon-to-carbonunsaturation is the ethylenic double bond, it is essential that theratio by weight of vinylidene compound to other monoethylenic monomer inthe reaction mixture shall be at least 5:95.

In preparing copolymers of polymerizable monoethylenic monomericvinylidene compounds having a molecular weight greater than 30 in whichthe sole aliphatic carbon-to-carbon unsaturation is the double bond inthe vinylidene group, in. the absence of other monoethylenic monomers,optimum results are obtained when at least one such vinylidene compoundis present in the reaction mixture in an amount at least equal to 5% ofthe total weight of vinylidene reactants.

The relative proportions of the monomer phase and the aqueous phase inthe aqueous systems of this invention are not necessarily fixed withinrigid limits. However, practically speaking, superior results areobtained with mixtures in which the ratio of the aqueous to thenonaqueous phase is within the range of from 0.921 to 10:1. In largescale operations, particularly, optimum results are obtained when theaforesaid ratio is within the range of from 1:1 to 4:1.

It is within the scope of this invention to employ aqueous mixturesproduced merely by agitation of the monomer phase with the aqueous phasebefore or during the polymerization period. It is not essential to thisinvention that dispersing agents be employed. However, the formation ofmore or less stable dispersions can be accomplished more readily throughthe agency of added dispersing agents, so that in many instances it isdesirable to use a dispersant. The choice of dispersing agent willdepend largely upon the properties of the monomers to be polymerized orthe pH of the aqueous medium. For example, the invention contemplatesconducting the polymerization in neutral, acid or alkaline aqueousvmedia. In neutral dispersions there may be used neutral dispersingagents of the type represented by polyvinyl alcohol, agar-agar, gelatin.methylated starch, sodium polymethacrylate, or the modified polymericdispersing agents derived from ethylene oxide. In alkaline media, it ispreferable to use dispersing agents of the type represented by alkalimetal or amine soaps of long chain fatty acids, for exampld, sodiumoleate, potassium laurate, or triethanolamine stearate. When dispersingagents are employed in acid media, it is essential that they be stableand will not decompose at pH values below 7. The preferred agents arethe synthetic dispersants comprising the soluble salts of long chainalkyl sulfates and sulfonates. Examples of this class are sodium cetylsulfate, the sodium salt of sulfonated paraflin white oil, and thesodium salt of sulfonated oleyl acetate. A wide variety of otherdispersing agents falling within this broad class are also suitable foruse in emulsifying the monomers of the invention in acid media. Hence,by selecting appropriate dispersing agents, the process of the inventioncan be conducted at pH values ranging from 1 to about 11. In the case ofmany monomers, however, superior polymers result when there are employedpH values in the range of about 3 to 5 and a dispersing agent which isstable under these conditions of mild acidity.

As hereinbefore stated the process of this invention is applicable toawide variety of monoethylenic compounds. Furthermore, the ratio ofaqueous to non-aqueous phases in the reaction mixture may be varied overrelatively wide limits; and dispersing agents may be employed or not(while the use of dispersing agents may 'be desirable in certaininstances, it is not essential to the successful operation of theprocess of this invention). It is, however, critical to this inventionthat there be employed a specific catalyst system, namely, anoxygen-liberating peroxy catalyst, of the type long known to beeffective in vinyl polymerizations, in combination with a sulfinic acidor an alkali metal salt thereof. As typical peroxy catalysts may bementioned hydrogen peroxide, benzoyl peroxide, diethyl peroxide, thealkali salts of percarbonic and perboric acid, and the soluble salts ofperdisulfuric acid, such as ammonium perdisulfate and the alkaliperdisulfates such as sodium and potassium perdisulfates. Any sulfinicacid (1. e., any alkyl or aryl sulfinic acid) may be used. Includedamong examples of alkyl sulfinic acids are methane sulfinic acid, ethanesulfinic acid, propane-alpha sulfinic acid, 2-hydroxyethane sulfinicacid, 2-methylpropane sulfinic acid, ethane-l,2-:disulflnic acid and thelike; while among examples of aryl sulfinic acids are benzenesulfinicacid, alpha-naphthalene sulfinic acid, beta-naphthalene sulfinic acid,diphenyl sulfinic acid, camphane sulfinic acid and the like. The acidsthemselves may be used, but it is often preferable to use their alkalimetal salts, e. g., their sodium, potassium, lithium, rubidium orcesium' salts, which are more soluble in water. A particularly effectiveagent is formamidine sulfinic acid which is produced by hydrogenperoxide oxidation of thiourea. The alkyl and aryl sulfinic acids aremade by known methods, for example, by reduction of the correspondingsulfonyl chlorides.

The amount of peroxy catalyst may be varied within relatively widelimits. Substantial results are obtained when the amount used is as lowas 0.01 based on the total weight of monoethylenic monomer and also whenit is as high as or more. The amount actually. used in any specificpolymerization will, of course, depend upon the polymerization aptitudeof the monomers, polymerization temperature and other factors which havean important bearing on the course of the reaction. In general it isbest to use the least amount of peroxy compound that will bring about asatisfactory rate of polymerization in a given type of equipment.Superior results are obtained with an amount of peroxy compound withinthe range of from 0.1% to 4%, and optimum results with an amount withinthe range of from 0.1% to 2% based on the weight of monoethylenicmonomer. 4

Similarly the amount of sulfinic acid or salt thereof used in thisinvention may be varied within relatively wide limits. Substantialresults are obtained when the amount employed is as low as 0.001% basedon the total weight of monoethylenic monomer present and when it is ashigh as 5% or more. the sulfinic acid or salt thereof is employed in anamount within the range of from 0.05% to 0.5% based on the total weightof monoethylenic monomer.

The ratio of peroxy compound to sulfinic compound employed has animportant bearing on the rate of polymerization of the monomers and inalmost every case this ratio must be adjusted carefully for maximumefficiency. In order to provide optimum' rates of polymerization andproducts having optimum properties, the ratio by weight of the peroxycompound to sulfinic acid or salt thereof in the reaction mixture shouldbe Superior results are obtained when within the range of from 0.5:1 to10:1. Frequently, the addition of the sulfinic acid or salt thereof tothe reaction mixture all at once is attended by a vigorous reaction asevidenced by a sharp increase in temperature and in such cases thesulfinic acid or its salt may be added portionwise to the reactionmixture during the course of the polymerization to prevent theoccurrence of undesirable fluctuations in temperature.

Broadlyspeaking polymerization may be conducted according to thisinvention at temperatures ranging from just above the freezing point ofthe dispersion, i. e., 0 C., to temperatures of C. and above, providedsuitable adjustments are made in the aqueous phase-monomer phase ratio,the concentration of the dispersing agent, if any is used, and theconcentration of peroxy catalyst and sulfinic compound.

Depending upon the conditions employed in the polymerization, thepolymers are obtained either as dispersions in water or as finelydivided suspensions. In either case, the polymers may be isolated asfinely divided powders by a variety of methods. For example, polymersprepared in the absence of added dispersing agents may be recovered by asimple filtration process followed by washing and drying in anappropriate equipment. On the other hand, if effective dispersing agentsar employed, the resulting permanent dispersion can be coagulated byfreezing, by the addition of suitable electrolytes or by spraying thedispersion into a heated and/or evacuated chamber. Generally speaking,the most satisfactory technique involves adding an appropriate amount ofan electrolyte to bring about coagulation of the polymers at atemperature just below the point where the precipitated polymers tend tocohere. This procedure yields a granular product which is readilywashed. Suitable electrolytes are sodium chloride, sodium sulfate,mineral acids, calcium chloride, inorganic nitrates, and aluminumsulfate. The washing and drying operation may be carried out by any ofthe procedures known to the art.

In conducting the polymerization of ethylenic compounds in aqueoussystems according to methods of the prior art, it often happens that thepresence of oxygen may have a retarding effect on the speed ofpolymerization. The effect of oxygen is minimized to a considerableextent in the process of the present invention, although in some casesit is desirable to displace air from the polymerization vessel by meansof an inert gas, such as nitrogen, carbon dioxide, methane or helium.The air may be removed by a simple flushing process or by repeatedlyintroducing the inert gas under pressure and purging until the lasttraces of oxygen originally present are substan tially eliminated.

The use of the combination of peroxy compound and sulfinic compoundaccording to this invention results in the polymerization ofmonoethylenic monomers either singly or in combination in a much shortertime with smaller proportions of catalyst than by the methods of theprior art. For example, many polymerizations which require 4 to 20 hoursaccording to the prior art methods can be accomplished within 15 minutesto one hour by using the combination of peroxy catalyst with a sulfiniccompound. This represents an important saving through increasingseveral-fold the amount of product that can be manufactured in a singleunit of equipment within a given period of time. Moreover, manycopolymer systems react with difiiculty according to the methods ofgeneous, more transparent and have higher softening points thancorresponding prior art copolymers.

The products prepared according to the present invention may be used inmoulded plastics, coatings, films, foils, fibers and adhesives. For anyof these purposes the polymer may be formed separately and thereaftercombined with, or may 5 be prepared in the presence of, plasticizers,stabilizers, fillers, pigments, dyes, softeners, natural resins orsynthetic resins. In the event the products had according to thisinvention are to be used as coatings or impregnating agents for porousmaterials, it is often practical to apply the poylmerized aqueousmixture directly to the material to be coated without the intermediateisolation of the polymer.

As many apparently widely diiferent embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that it is not limited to the specific embodiments thereofexcept as defined in the app ended claims.

Having described the present invention, the following is claimed as newand useful:

1. In a process of polymerizing monoethylenic monomers havingavmolecular weight greater than 30 in which the sole aliphaticcarbon-tocarbon unsaturation is the ethylenic double bond and of whichnot less than 5% by weight is a polymerizable vinylidene compound havinga molecular weight greater than 30 in which the sole aliphaticcarbon-to-carbon unsaturation is the double bond in the terminalvinylidene radical, the improvement which consists in subjecting from 5%by weight of vinylidene compound in admixture with anotherof saidmonoethylenic monomers to 100% by weight of said vinylidene compound, inan aqueous medium containing from 0.01% to 5% of an oxygen-yieldingpolymerization catalyst and from 0.001% to 5% of a member of the groupconsisting of sulfinic acids and alkali metals salts thereof, based onthe total weight of monomer, to a temperature of from C. to 125 C. untilpolymerization has taken place.

2. In a process of polymerizing polymerizable monoethylenic monomericvinylidene compounds having a molecular weight greater than 30 in whichthe sole aliphatic carbon-to-carbon unsaturation is the double bond inthe terminal vinylidene radical, the improvement which consists insubjecting from one to two of said monomers, in an aqueous mediumcontaining from 0.01% to of an oxygen-yielding polymerization catalystand from 0.001% to 5% of a member of the group consisting of sulfinicacids and alkali metal salts thereof, based on the total weight ofmonomer, to a temperature of from 0 C. to 125 C, until polymerizationhas taken place.

3. In a process of polymerizing a mixture of polymerizable monoethylenicmonomeric vinylidene compounds having a molecular weight greater than 30in which the sole aliphatic carbon-to-carbon unsaturation is the doublebond in y C. until polymerization has taken place.

4. In a process of polymerizing a polymerizable monoethylenic monomericvinylidene compound having a molecular weight greater than 30 in whichthe sole aliphatic carbon-to-carbon unsaturation is the double bond inthe terminal vinylidene radical, the improvement which consists insubjecting said vinylidene compound, in an aqueous medium containingfrom 0.01% to 5% of an oxygen-yielding polymerization catalyst and from0.001 to 5% of a member of the group consisting of sulfinic acids andalkali metal salts thereof, based on the total weight of the vinylidenecompound, to a temperature of from 0 C. to 125 C. until polymerizationhas taken place,

5. A process according to claim 4 wherein the aqueous medium containsfrom 0.1% to 4% of oxygen-yielding polymerization catalyst and from0.05% to 0.5% of a member of a group consisting of sulfinic acids andalkali metal salts thereof based on the total weight of the vinylidenecompound and the ratio of the aqueous to the nonaqueous phase is withinthe range of from 0.9:1 to 10:1.

6. A process according to claim 4 whereinthe aqueous medium containsfrom 0.1% to 2% of an oxygen-yielding polymerization catalyst and from0.05% to 0.5% of a sulfinic compound of the group consisting of sulfinicacids and alkali metal salts thereof based on the total weight of thevinylidene compound, the ratio of said peroxy compound to said sulfiniccompound being within the range of from 0.521 to 10:1 and the ratio ofthe aqueous to the non-aqueous phase being within the range of from 1:1to 4:1.

7. In a process of polymerizing an ester of an alpha, beta-unsaturatedmonocarboxylic acid in which said alpha,beta-unsaturation is a terminaldouble bond and is th sole aliphatic carbon-tocarbon unsaturation, theimprovement which consists in subjecting said ester in an aqueous mediumcontaining from 0.01% to 5% of an oxygen-yielding polymerizationcatalyst and from 0.001% to 5% of a sulfinic compound of the groupconsisting of sulfinic acids and alkali metal salts thereof, based onthe total weight of said ester,

to atemperature of from 0 C. to C. until polymerization has taken place,the ratio of oxygen-yielding polymerization catalyst to sulfiniccompound in the reaction mixture being within the range of from 0.521 to10:1 and the ratio of the aqueous to the non-aqueous phase in the saidmixture being within the range of from 0.911 to 10:1.

8. A process according to claim 7 wherein the ester is methylmethacrylate, the oxygen-yielding polymerization catalyst is hydrogenperoxide, the sulfinic compound is sodium p-toluenesulfinate and theratio of the aqueous to the non-aqueous phase in the reaction mixture iswithin the range of from 1:1 to 4:1.

9. In a process of polymerizing a vinyl ester of a saturatedmonocarboxylic acid the improvement which consists in subjecting saidvinyl ester in an. aqueous medium containingfrom 0.01% to 5% of anoxygen-yielding polymerization catalyst and from 0.001% to 5% of asulfinic compound of the group consisting of sulfinic acids and alkalimetal salts thereof, based on the total weight of the vinyl ester, to atemperature of from C. to 125 C. until polymerization has taken place,the ratio of oxygen-yielding polymerization catalyst to sulfiniccompound in the reaction mixture'being within the range of from 0.5:1 to:1 and the ratio of the aqueous to the non-aqueous phase in the saidmixture being within the range of from 0.9:1 to 10:1.

10. In a process of polymerizing vinyl acetate the improvement whichconsists in subjecting said compound in an aqueous medium containingfrom 0.1% to 2% of hydrogen peroxide and from 0.05%

to 0.5% of formamidine sulfinic acid, based on the total weight of thevinyl acetate, to a temperature of from 0 C. to 125 C. untilpolymerization has taken place, the ratio of hydrogen peroxide toformamidine sulfinic acid in the reaction mixture being within the rangeof from 0.5:1 to 10:1 and the ratio of the aqueous to the non-aqueousphase in the said mixture being within the range of from 0.921 to 4:1.

11. In a process of polymerizing an alpha,betaunsaturated nitrile inwhich said alpha,beta-unsaturation is a terminal double bond and is thesole aliphatic carbon-to-carbon unsaturation, the improvement whichconsists in subjecting said nitrile in an aqueous medium containing from0.01% to 5% of an oxygen-yielding polymerization catalyst and from0.001% to 5% of a sulfinic compound of the group consisting of sulfinicacids and alkali metal salts thereof, based on the total weight of thenitrile, to a temperature of from 0 C. to C. until polymerization hastaken place, the ratio of the oxygen-yielding polymerization catalyst tosulfinic compound in the reaction mixture being within the range of from0.5:1 to 10:1 and the ratio of the aqueous to the non-aqueous phase inthe said mixture being within the range of from 0.9:1 to 10:1.

12. In a process of polymerizing acrylonitrile the improvement whichconsists in subjecting said compound in an aqueous medium containingfrom 0.1 0 to 2% of ammonium perdisulfate and from 0.0 to 0.5% of sodiump-toluenesulfinate, based on the total weight of the acrylonitrile, to atemperatureof from 0 C. to 125 C., until polymerization has taken place,the ratio of ammonium perdisulfate to sodium p-toluenesulflnate in thereaction mixture being within the rang of from 0.5:1 to 10:1 and theratio of the aqueous to the non-aqueous phase in the said mixture beingwithin the range of from 1:1 to 4:1.

WINIFRED M. JACOBSON. Executrix of the Estate of Ralph Albert Jacobson,

- Deceased.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,419,010 Cofiman et a1. Apr. 15,1947

1. IN A PROCESS OF POLYMERIZING MONETHYLENIC MONOMERS HAVING A MOLECULARWEIGHTG GREATER THAN 30 IN WHICH THE SOLE ALPHATIC CARBON-TOCARBONUNSATURATION IS THE ETHYLENIC DOUBLE BOND AND OF WHICH NOT LESS THAN 5%BY WEIGHT IS A POLYMERIZABLE VINYLIDENCE COMPOUND HAVING A MOLECULARWEIGHT GREATER THAN 30 IN WHICH THE SOLE ALIPHATIC CARBON-TO-CARBONUNSATURATION IS THE DOUBLE BOND IN THE TERMINAL VINYLIDENE RADICAL, THEIMPROVEMENT WHICH CONSISTS IN SUBJECTING FROM 5% BY WEIGHT OFVINYLIDENCE COMPOUND IN ADMIXTURE WITH ANOTHER OF SAID MONETHYLENICMONOMERS TO 100% BY WEIGHT OF SAID VINYLIDENCE COMPOUND, IN AN AQUEOUSMEDIUM CONTAINING FROM 0.01% TO 5% OF AN OXYGEN-YIELDING POLYMERIZATIONCATALYST AND FROM 0.001% OF 5% OF A MEMBER OF THE GROUP CONSISTING OFSULFINIC ACIDS AND ALKALI METALS SALTS THEREOF, BASED ON THE TOTALWEIGHT OF MONOMER, TO A TEMPERATURE OF FROM 0* C. TO 125*C. UNTILPOLYMERIZATION HAS TAKEN PLACE.